Since the discovery of neuroglia by Virchov it has become increasingly clear that glial cells play an important role in the modulation of the synaptic environment, by virture of their ability to accumulate neuroactive substances as well as ions. The proposed studies are aimed firstly at delineating the kinetic parameters, pharmacology and ionic requirements of norepinephrine (NE), dopamine (DA) and serotonin (5HT) transport by normal glial cells, using splices of the frog filum terminale (FT). The FT is the terminal portion of the spinal cord caudal to the last root which consists largely of glia, and which we have shown to be a normal glial preparation useful for the study of glial transport. The experiments utilizing slices of the FT preparation will be complimented by those using normal glia astrocytes grown in culture. Fundamental to an understanding of neuronal-glia interrelationships in vivo are insights as to whether glial cells can release neurotransmitter substances in response to changes in ionic environment. It is therefore proposed to study the release of preloaded 3H NE, DA, 5HT and GABA from slices of the FT in response to superfusion by media containing depolarizing concentrations of K+ and to determine to what extent such processes are similar to those present in neurons. In the terminal portion of the developing tadpole spinal cord the rates of GABA accumulation change concomitantly with metamorphosis and the neuronal degeneration and in the adult frog where surgical transection of all descending inputs to the FT results in changes in GABA and 5HT accumulation. These data strongly suggest that glial membrane properties are plastic, and respond to changes in the glial microenvironment. Therefore the accumulation of 5HT, NE, and DA will be studied in slices of the terminal portion of the tadpole cord as a function of development and in adult frogs in which descending input to the FT has been transected. The sites of uptake will be verified by EM radioautography and immunocytochemistry. Total or cell type specific glial changes will be monitored by use of radioimmunoassays based on availability, both monoclonal or produced in rabbits, to the S-100 and GFA proteins, as well as to glycophosphate dehydrogenase and myelin basic protein.